The present invention relates to an automatic cooking control system for a microwave oven which automatically cooks foods contained in a heating chamber by utilizing a temperature sensor. More specifically, the present invention relates to an automatic cooking control system for a microwave oven which allows cooking of foods by correctly establishing the heating period of time of the foods even when the temperature of the incoming air, flowing into a heating chamber via a fan, is varied due to the ambient temperature around the microwave being raised or lowered.
A conventional microwave oven, as shown in FIG. 1, is constructed with a microcomputer 1 which controls the whole operation of a microwave oven; a power source 2 which supplies electric power source according to the control of magnetron 3 which generates microwave energy according to the output power from the power source 2; a heating chamber 4 which heats the foods with the microwave energy generated from the magnetron 3; a fan 5 which causes air to flow through an air inlet 4A of the heating chamber 4; a temperature detecting sensor 6 which detects the temperature of the air flowing through an air outlet 4B of the heating chamber 4; and an analog/digital converter 7 which receives the temperature signal of the outflow air detected by the temperature detecting sensor 6 and converts the signal into a digital signal.
Conventional microwave oven as described above, a user begins the cooking process by putting the foods to be cooked into the heating chamber 4 and and then presses a buttom to start the cooking, as shown in FIGS. 2 and 3. A microcomputer 11 then performs an initial operation for a certain period of time t.sub.1. During this initial operation, the air temperature within the heating chamber 4 is caused to become uniformly balanced with the air flowing through the air inlet 4A into a heating chamber 4 by actuating the fan 5 for about 16 seconds. At this moment, the temperature of the air flowing through the air outlet 4B of the heating chamber 4 is detected by the temperature detecting sensor 6 from. The detected temperature signal is converted into digital signals by an analog/digital converter 7 to produced an output.
When a certain period of time elapses under this condition the microcomputer 1 stores the signal of the present temperature T.sub.1 received from the analog/digital converter 7 and utilizes this signal to control the electric power source 2 which actuates the magnetron 3. When the magnetron 3 is actuated, the magnetron 3 generates microwave energy which heats up the food contained in the heating chamber 4 since the temperature of the air flowing out of the air outlet 4B of the heating chamber 4 is raised gradually raised according to the heating of the food, the detected temperature signal which is detected by the temperature detecting sensor 6 gradually becomes raised.
When an increment of temperature, which is caused under these condition, reaches a certain temperature value .DELTA.T, i.e., if the increment of the temperature becomes a certain temperature value .DELTA.T due to the temperature detected by the temperature detecting sensor 6 is raised to a certain temperature T.sub.2, the microcomputer 1 finishes a first step of the heating process and begins to execute a second step of heating the process. That a period of time t.sub.2 realized during the first heating stage is stored, then a constant value .alpha. established in accordance with the kind of food being cooked is multiplied by the period of time t.sub.2 ' thereby calculating a period of time t.sub.3 to be used during the second heating stage calculated, and. The food is heated by continuously actuating the magnetron 3 during the period of time t.sub.3. When the heating stage period of time t.sub.3 has elapsed, the operation magnetron 3 and of the fan 5 are scopped, and the cooking of the food is completed.
However, in such a conventional automatic cook control system as described above, the automatic cooking of foods could not be precisely performed because when the temperature of the air flowing into a heating chamber 4 is varied due to the ambient temperature around the microwave oven during the performing of the first heating stage, the temperature detected by the temperature detecting sensor 6 also varied in accordance with the variation of the temperature.
As shown in FIG. 4A, if the temperature of the air that the fan 5 blows into the heating chamber 4 is raised, according to the rise in the external temperature, as much as a temperature value .DELTA.T1 during the first heating stage the temperature detected at the temperature detecting sensor 6 rises as much as an amount of a certain temperature value .DELTA.T2 in accordance with the rise of the temperature. Accordingly the period of time t.sub.2 realized during the first heating stage in advanced by a certain period of time .DELTA.t.sub.2 ; therefore, the cooking of the food is not completely finished. Further as shown in FIG. 4B, if the temperature of the air that the fan 5 blows into the heating chamber 4 drops as much as a certain amount of temperature value .DELTA.T'.sub.1 in accordance with a drop in the ambient temperature, the temperature which is detected by the temperature detecting sensor 6 down as much as a certain amount of temperature value .DELTA.T'.sub.2. Accordingly, the period of time t.sub.2 realized during the first heating stage is delayed by a certain period of time .DELTA.t'.sub.2 ; therefore, the automatic cooking causes over cooking of the foods.
In addition, in the conventional automatic cooking method described above, an error occurs when establishing a heating period of time in accordance with the ambient temperature around the microwave oven due to the variation in the seasons. Even though same kind, and amount of food is heated, when the ambient temperature is a temperature representative of spring or autumn, a constant temperature varying charateristic is obtained. While when the ambient temperature is representative of summer, the temperature increasing rate becomes nonexistent when compared to the rate in spring or autumn, and when the ambient temperature is low as in winter, temperature increasing rate is higher than in spring or autumn. As a result, if a predetermined constant temperature increment .DELTA.T is established of time the heating period of time of the foods is incorrectly established in accordance with the ambient temperature around the microwave oven due to the variation in the seasons; therefore, there has been also the defectiveness the food is either overcooked or undercooked.